Some complex voice scramblers used by the U.S. Armed Forces transmit preambles before passing the voice signal. It is usually necessary that the communicator key the scrambler and then wait for the preamble to be transmitted before he speaks. Also where "full duplex" operation is used that provides separate frequency for transmitting and receiving, it is desirable for more efficient operation to remove any delay caused by the transmission of a preamble or a postamble.
The present invention provides a voice-controlled disappearing audio delay line control circuit so that a "hot mike" voice circuit can be fed into a voice scrambler. The operator then need not key the scrambler. There is no waiting for the preamble transmission before speaking. The voice scrambler can be remote from the operator with no intervening special control lines, since only the voice signal is required to control the scrambler.